Modern semiconductor electronic device packages such as integrated circuit (IC) chips are typically formed by building multiple layers of materials and components on a semiconductor substrate. A single wafer will contain a plurality of individual ICs or dies, which are later separated following fabrication by a cutting process referred to in the art as singulation or dicing. The semiconductor devices incorporate numerous electrically active components which are formed in multiple layers of an electrically insulating or dielectric material. Metal conductors or interconnects are formed in the dielectric material by various additive patterning and deposition processes (e.g. damascene and dual damascene) to electrically couple active components together in the different layers and/or within a single layer. Modern semiconductor fabrication, accordingly, entails a repetitive sequence of numerous process steps including material deposition (conductive metals and non-conductive materials), photolithographic patterning of circuits in the deposited material, and selective material removal such as etching and ashing to gradually build the semiconductor device structures.
Some of the foregoing semiconductor fabrication processes are performed in commercially-available vacuum processing tools or machines. These semiconductor processing machines include a heated vacuum process chamber that holds one or more wafers and a vacuum source fluidly connected to chamber. These semiconductor fabrication tools generally further include a gas supply system for introducing reactant process gases to the chamber that may be used for conventional etching/ashing processes which remove semiconductor materials from the wafer or vapor deposition processes (e.g. CVD, PVD, etc.) which add layers of thin films or materials to the wafer. The vacuum source reduces the pressure in the process chamber and exhausts or draws gases from the chamber to establish flow from the chamber to the vacuum sources. The vacuum source for the process chamber is typically provided by a vacuum pump that is fluidly connected to the process chamber via vacuum exhaust piping and valving.
FIG. 1 shows an example of one known conventional vacuum processing machine or system 10 and vacuum piping arrangement. Processing system 10 includes a vacuum process chamber 11, gas supply system 13, vacuum pump 14, vacuum pumping piping 15 from process chamber 11 to vacuum pump 14, and single combination pressure control and isolation valve 14. Process chamber 11 holds one or more wafers W supported by base 12. The vacuum pumping piping 15 shown has four inlets 19 which are coupled to pumping ports in vacuum process chamber 11 located proximate to each wafer W. The desired vacuum pressure in process chamber 11 is maintained by measuring the actual chamber pressure P via a pressure gauge or sensor 17 and sending a corresponding digital or analog pressure signal to a pressure controller 18. The pressure controller 18 compares the actual chamber pressure P to a predetermined desired chamber setpoint pressure Ps. If the variance between actual and setpoint pressures exceed a predetermined threshold limit, the controller 18 sends a signal to throttle the pressure control-isolation valve 14 until the actual chamber pressure P is brought back into the desired pressure range.
The foregoing conventional vacuum processing systems, however, are prone to a number of problems. The asymmetric vacuum pumping piping 15 arrangement and multiple piping branches may result in unbalanced vacuum pressures in each branch and/or piping inlets 19 and corresponding portions of the process chamber 11. This in turn may lead to an uneven gas flow pattern through the process chamber causing non-uniform material removal or deposition either on a single wafer or wafer-to-wafer leading to higher than normal die reject rates. Although these effects may be less pronounced when processing 300 mm or smaller wafers, the flow and pressure imbalance becomes a more significant problem for processing the larger next generation 450 mm size wafers. Furthermore, the multiple branches and complex configuration of the vacuum pumping piping 15 increases flow resistance resulting in lower pumping efficiency and higher operating costs.
Another problem with the foregoing known vacuum processing systems 10 is the accumulation or buildup of solid process byproducts (e.g. powders, residues, particles, etc.) in the vacuum pumping piping 15 that carry over from the semiconductor material removal or deposition processes performed in vacuum chamber 11. The particulate byproduct buildup reduces the effective internal diameter of the vacuum piping, raises back pressure on the vacuum chamber 11, and decreases gas flow leading to higher byproduct accumulation rates in the piping. The decreased internal piping diameter increases flow resistance and decreases pumping efficiency as well. In addition, the particulate byproduct accumulations further exacerbate the pressure balance problems and uneven gas flow in the process chamber mentioned above that leads to non-uniform wafer material removal and deposition. Frequent periodic maintenance and downtime of the vacuum process machine is required to disassemble the vacuum pumping piping 15 and remove particulate byproduct buildups.
Existing piping arrangements having numerous horizontal piping sections such as the vacuum pumping piping 15 shown in FIG. 1 are particularly susceptible to increased buildup of semiconductor fabrication process particulate byproducts. The horizontal sections of existing pumping piping arrangements act as ledges or traps for particulate matter to accumulate, and is particularly pronounced near the piping inlets 19 beneath the pumping ports on process chamber 11 as shown in FIG. 2. The flow eddies and stagnant flow regions caused by the many piping bends, particularly 90 degree elbows, also create low flow regions where particulate byproduct buildup tends to occur.
Yet another problem with the foregoing known vacuum processing systems 10 is inability to compensate for the uneven gas flow due to vacuum pressure imbalances in the vacuum pumping piping 15 resulting from the asymmetrical piping arrangement and particulate byproduct buildup in the piping. Only a single pressure measurement of the process chamber actual pressure P is recorded giving the controller and/or process operating personnel no information on whether one of the piping branches may have partial blockages due to particulate byproduct buildup causing the uneven gas flow. Furthermore, because only a single combined pressure control-isolation valve 14 is provided, the controller or operator has no real ability to balance the gas flow and pressures from side to side in the piping branches to compensate for excessive buildup occurring in one of the branches. Therefore, the entire processing machine must be shut down for maintenance to clean out the particulate buildup.
An improved vacuum processing machine piping arrangement and pressure monitoring and control system is therefore desired.